Safety and/or security documents, identity cards, passports, ID cards, access control cards, visas, control characters, tickets, driver's licenses, motor vehicle documents, bank notes, checks, postage stamps, credit cards, any smart cards and adhesive labels (e.g. for product protection) often comprise at least one substrate and a partially or completely transparent cover layer. Substrate and cover layer may in turn consist of a plurality of layers. To make forgery of such documents more difficult, they are equipped with security elements. For example, bank notes and postage stamps may consist of one substrate or substrate layer only, to which security elements can then be applied, for example in the form of a printing ink. Some security elements include substances being luminescent under certain physical conditions, and a verification can be carried out by visual inspection or automatic detection of the luminescence under these conditions.
Security elements of the type mentioned are known in the art, for example from the documents WO 2005/115766 A1 or WO 2010/006583. Particulate luminescent substances are used, which may be encapsulated, i.e. have a core/shell structure. These core/shell structures are embedded in a polymeric matrix. In general, the substances having the electroluminescent properties are always present in a particulate form, with particle sizes above 200 nm.
A disadvantage of the security elements known so far is the relatively low luminescence obtained under given excitation conditions and the high cost of production of core/shell structures.
From the document EP 0688839 A2, polycarbonates based on a geminally disubstituted dihydroxydiphenyl cycloalkane are per se known. In this prior art, such polycarbonates are used as binders for screen-printing inks. This document also describes methods for making such polycarbonates.